Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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118
FXUS62 KRAH 102025
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
325 PM EST Sat Dec 10 2016

.SYNOPSIS...
High pressure will settle overhead through tonight, then shift
offshore Sunday. A warm front will push northward through the area
Sunday night, and then a cold front will move through the region
Monday night, before stalling out across the Carolinas through mid
week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 140 PM Saturday...

Another quiet and cold night ahead as a portion of arctic high
pressure slides across the Mid Atlantic region tonight. While the
vast majority of the column is very stable and dry, areas of high
level clouds from the mid Miss Valley will track within fast zonal
steering flow eastward across VA and northern NC this evening into
the overnight hours, yielding fair to briefly partly cloudy skies
across the northern forecast area tonight. Some of these clouds may
exhibit a period of orographic enhancement, although the moisture
aloft may not be sufficient, and the upper level wind direction is a
bit more westerly than is ideal. Otherwise, these high clouds should
be mostly thin with limited coverage, and as such will have minimal
impact on radiational cooling with otherwise mostly clear skies and
very light winds. Lows 18-25, coldest in rural Piedmont areas. -GIH

&&

.SHORT TERM /Sunday through Sunday night/...
As of 235 PM Saturday...

The surface high will shift off the Mid Atlantic coast Sunday with
frontogenesis taking place along the Carolina coast. Moist
overrunning flow focused on the 285-290K layer will surge northward
through the area Sun afternoon, resulting in a south-to-north trend
to mostly cloudy skies, which will last through Sun night. The
precip details are tough to resolve, given the lack of agreement
among the large scale models as to the coverage and amounts through
Sun night. The NAM brings very light precip into the NC Foothills
Sun afternoon, whereas the GFS has patchy light rain over the
Sandhills, and the ECMWF is dry. Heading through Sun night, the
ECMWF remains mostly dry (sandwiched between showers and the coast
and light rain in the NC/VA Foothills), while the GFS brushes light
precip over our far eastern sections and the NAM -- which has much
deeper saturation -- drops heavier rain farther west to Highway 1.
The SREF QPF plumes show most members have no precip or just very
light amounts, around 0.01". Given the expected presence of dry air
above the freezing level and fairly shallow nature of the moist
upglide, have kept pops mostly in the slight chance range, for light
rain or drizzle, although I have retained a period of 25-30% pop in
the east for a portion of Sun night. Expect highs of 45-51 Sun,
coolest NW and warmest SE, followed by a "low" of 39-47 Sun night,
with temps dipping early in the evening then holding steady or
rising slightly overnight as the warm air just aloft spreads in. -GIH

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
As of 325 PM SATURDAY...

Not a lot of confidence in the long term forecaster this afternoon.
Monday will begin with a low pressure system over the Great Lakes
with a cold front stretching southward through the Mississippi
Valley. Temperatures will warm with southwesterly flow ahead of this
front and so Monday and Tuesday will both see temperatures in the
mid 50s to mid 60s NW to SE. Frontal passage should actually occur
Monday night early Tuesday with some light rain associated with it.
On Tuesday we could see another chance for rain with a wave coming
up from the south but accumulations for this event will not be very
high for either event and are expected to be all liquid as low temps
as temperatures Monday night and Tuesday night should stay mostly in
the 40s with some upper 30s across the NW Piedmont.

A couple more southern waves may affect southern counties on
Wednesday and Wednesday night again with minimal all liquid
accumulations. Temps on Wednesday will be in the 50s with lows in
the upper 20s to mid 30s with the sub-freezing temperatures occurring
in the NW after the precipitation has already moved out. Thursday
and Friday will be dry and cold with temps in the upper 30s to low
40s.

Very low confidence forecast for Friday night into Saturday morning
however, there is a slight chance that there will be a short window
for some freezing rain across the northern counties early Saturday
morning if freezing temperatures and precipitation overlap. Right
now there is a huge spread in the models in both temperature and
precipitation values. The only thing that is fairly high confidence
is that if, and that is a big if, we have any precipitation type
problems, it will most likely be freezing rain. Stay tuned.

&&

.AVIATION /18Z Saturday through Thursday/...
As of 100 PM Saturday...

High confidence in VFR conditions through at least 15z Sun. High
pressure will settle over the region today into tonight, before
shifting off the Mid Atlantic coast on Sunday. Deep dry air remains
in place, and any clouds through daybreak Sunday will be very high
(above 15,000 ft AGL) with unrestricted vsbys and light surface
winds. Then, as a warm front begins to push northward into the
region, MVFR clouds will start to spread into NC from south to north
after about 15z. Cigs are expected to drop to MVFR at FAY near the
very end of the TAF valid period, but cigs should stay VFR elsewhere
through 18z Sun.

Looking beyond 18z Sun, MVFR cigs will continue spreading northward
through NC Sun afternoon. Cigs should then drop to IFR after sunset,
with a good chance for low level wind shear developing after
midnight, as 1500-1800 ft AGL winds will be from the SW at 35-40 kts
but under 10 kts at the surface. Areas of light rain will also
develop overnight, with period MVFR vsbys along with the IFR cigs,
as the warm front stalls over the area. Unsettled sub-VFR conditions
should dominate from Mon into Wed as the front stalls out over the
Carolinas with weak waves of low pressure tracking along it,
although the details on timing of such adverse conditions are highly
uncertain. The front should finally push back well to our south
early Thursday, with a trend back to VFR as high pressure pushes in
from the north. -GIH

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

SYNOPSIS...Hartfield
NEAR TERM...Hartfield
SHORT TERM...Hartfield
LONG TERM...Ellis
AVIATION...Hartfield



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